Direct dating of mid-crustal shear zones with synkinematic allanite:new in situ U-Th-Pb geochronological approaches applied to the Mont Blanc massif

International audienceDating the timing of motion on crustal shear zones is of tremendous importance for understanding the assembly of orogenic terranes. This objective is achieved in this paper by combining petrological and structural observations with novel developments in in situ U-Th-Pb geochronology of allanite. A greenschist facies shear zone within the Mont Blanc Massif is documented. Allanite is synkinematic and belongs to the mylonitic assemblage. LA-ICP-MS U-Th-Pb isotope analyses of allanite reveal high contents and highly radiogenic isotopic compositions of the common-Pb component. The use of measured Pb-isotope compositions of associated minerals (feldspars and chlorite) is critical for accurate common-Pb correction, and provides a powerful mechanism for linking allanite growth to the metamorphic assemblage. A mean 208Pb/232Th age of 29.44 ± 0.95 Ma is accordingly taken for synkinematic allanite crystallisation under greenschist facies conditions. This age reflects the timing of the Mont Blanc underthrusting below the Penninic Front and highlights the potential of directly dating deformation with allanite

On the Fixed Points of Abelian Group Automorphisms

In this article, we present general properties of fixed-point groups of the automorphisms of finite groups. Specifically, we determine the form of fixed-point groups and partition \aut(G) according to the number of fixed points possessed by each automorphism. A function $\theta$ records the size of each partitioning set; we find properties for $\theta$ in general and develop formulae for $\theta$ with respect to certain classes of finite abelian groups

Emergent Learning: A Framework for Whole-System Strategy, Learning, and Adaptation

The field of philanthropy is exploring what it takes to achieve impact in complex environments. The terms “adaptive” and “emergent” are beginning to be used, often interchangeably, to describe strategies by which funders can tackle complexity. This article proposes distinguishing between the two and explores more deeply how the research into complexity can inform philanthropic practice. While approaches like systems mapping, scenario planning, and appreciative inquiry have been put forward as useful approaches to expanding perspectives and seeing whole systems, the field needs a framework for going beyond these planning tools in order to actually create the conditions in which emergence can happen – by expanding agency beyond the walls of the funder, distinguishing between goals and strategies, encouraging experimentation around strategies, and supporting whole-system learning, which requires shorter, faster, more rigorous real-time learning and more cross-pollination among peers. This article offers Emergent Learning as a framework to support the creation of these conditions and describes how the tools help make thinking visible and support real-time and peer learning. It looks at two organizations that have embraced Emergent Learning to support a more emergent approach to achieving a whole that is greater than the sum of its parts

Method and apparatus for rate integration supplement for attitude referencing with quaternion differencing

A control system for providing attitude control in spacecraft. The control system comprising a primary attitude reference system, a secondary attitude reference system, and a hyper-complex number differencing system. The hyper-complex number differencing system is connectable to the primary attitude reference system and the secondary attitude reference system